1971 9.8 110 only run at high revs (no idle)

[Shetland 535]

Old non runner came with boat. Clean fuel, primed cylinders, heated plugs , changed carb gaskets, checked fuel pump diaphragm looked ok but didn't replace, got it running but no water flow. Have just replaced impeller and key now urinating like a racehorse!
Good even compression across cylinders approx 108
Will only start after choking/flooding carb then will run with choke off but with throttle quite wide open only (hi revs)
Is my first port of call new fuel pump diaphragm and integrity of fuel lines?
When you decrease revs you can hear engine failing to fire then when you open throttle it will kick in sounding healthy. No backfiring or spluttering, just all or nothing, any ideas would be greatly received. Thanks people

 

[MH Hawker]

Re: 1971 9.8 110 only run at high revs (no idle)

Yep the idle circuit in the carb is plugged up but the main is still open. Time for a first class rebuild.

 

[Bondo]

Re: 1971 9.8 110 only run at high revs (no idle)

Yep the idle circuit in the carb is plugged up but the mail is still open. Time for a first class rebuild.

Ayuh,.... Welcome Aboard, Shetland 535,..... I agree with MH Hawker,.....

Sounds more like a plugged up Carb, than a failin' fuel pump to me,...

 

[oldman570]

Re: 1971 9.8 110 only run at high revs (no idle)

Yep, sure sounds like the carb needs a very good cleaning and rebuild. As long as the motor is running at high revs, the ignition wiring must still be in good shape. You never want to mess with the points on the older motors unless you absolutely have to. They can be a PITA to get set correct. If there is any brittle insulation on the wires for the ignition, they should be replaced along with the nylon inserts for their terminals under the flywheel. The wires can short out an cause trouble when the stator plate is moved when giving the motor fuel. This is just a heads up for other troubles you can run into. JMO
Oldman570

 

[Shetland 535]

Re: 1971 9.8 110 only run at high revs (no idle)

Really appreciate the feedback here. Idle jet was clean.....but the little gasket that sits under the flange was missing which I guess Affects the seal. Hasn't made a great deal of difference, plus I put a new set of plugs in after putting the carb back together. Got it running, still a little reluctant to tick over tho managed to get it down there a few times and keep it running. But then it just flat out dies, can happen higher in the rev range too. One new observation once it warmed up a little, noticed a tiny bit of bubbling/liquid discharge from a small area, maybe 1/8 th inch long on the crankshaft cover to block gasket seal. I guess this means it's blown and if liquid is getting out, air must be too, which would affect fuel pressure across crank and up into pistons.
Once it got warm also started misfiring, kicking and spluttering a lot more.
I'm presuming new gasket, slowly finding the flaws on an old dried up, but yet workable lump.
What do you think people?

 

[MH Hawker]

Re: 1971 9.8 110 only run at high revs (no idle)

Their is a lot more to cleaning a carb that just the jets, you also need to make sure all of the very small passages are clean, i use the spray can cleaner and a air compressor, then i use a piece of mono fishing line and run it through to just make sure and then once back in use i use seafoam in the tank at a 2 oz per gallon mix for a few tank fulls. I hate doing the same job over and over.

I am sure you will get it working fine but it often takes a bit of work and time.

 

[racerone]

Re: 1971 9.8 110 only run at high revs (no idle)

Perhaps the lower crankshaft seal is also bad.-----Not hard to give this motor a complete inspection / repairs.

 

[oldman570]

Re: 1971 9.8 110 only run at high revs (no idle)

^1 0n Racers reply. Any leak in any of the gaskets and seal on the crank case will make the motor a pain, if not impossible to get the motor running correctly. Not to mention that the motor can run on a lean fuel mixture and only cause more damage. As long as one has the time, knowledge, and $$$ to repair the motor, then go for it. It can only end in frustration or a very good running motor, along with the great feeling that you know you have accomplished something a lot of others have not. Do not let others be your downfall,and go for it. JMO
Oldman570

 

[racerone]

Re: 1971 9.8 110 only run at high revs (no idle)

Working on a 1974 Evinrude 9.9 HP right now.-----------Had been worked on by someone.-----------Had a blown bottom crankshaft seal.-----Of course it had a new fuel pump / new thermostat / overhauled carburetor.---------I can not believe that folks think that a 40 year old motor can be revived with a couple of new sparkplugs and a new fuel pump.